Download Enceladus is small (500 km diameter)

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Life on
Titan?
Enceladus
Enceladus is small
(500 km diameter)
Young, crater-free surface
regions with like those on Europa
Orbit resonance with Dione
South polar hot spot and ice
plumes
Thin “atmosphere” of water
vapor
Subsurface ocean!?
Enceladus
Ice Plumes from Enceladus
Area of plumes is much
warmer than surroundings evidence of subsurface
reservoir of liquid water
Enceladus feeds
the outer E ring
Most likely, there is
subsurface liquid water,
simple organics, and
water vapor welling up
from below.
Over billions of years,
heating of this cocktail of
simple organic molecules,
water, and nitrogen could
have led to some of the
most basic building blocks
of life.
Moons of Uranus
No large moons, nothing of
particular interest as far as
the search for life
Named moons of Uranus
Cordelia
Ophelia
Bianca
Cressida
Desdemona
Juliet
Portia
Rosalind
Belinda
Puck
Miranda
Ariel
Umbriel
Titania
Oberon
Caliban
Sycorax
Prospero
Setebos
Stephano
Trinculo
What do these
names have in
common?
They are all
characters from
the works of
Shakespeare &
Alexander Pope
Moons of Neptune
One location of interest
• Neptune’s Triton
– Extremely cold (< 40K)
objects made from
volatile materials
produce icy volcanism.
– Huge geysers of
nitrogen!
– Pluto and the Kuiper
Belt Objects may look
and act similarly.
Very unlikely location for life
Solar system beyond Saturn
• Decline of probability of life
– Main factor is temperature
– Europa  Ganymede  Callisto  Titan  Enceladus ?
• Triton
– Retrograde rotation  capture
– Uneven surface:
• Cantaloupe terrain, Smooth parts, Frost deposits?, Wind
streaks
– Few impact craters  recent geological activity (10100 Myr)
• Pluto and remaining moons
– Too cold and too small
– But, amino acids seen in meteorites
Time to reach for the stars!
Star
A mass of gas held
together by gravity
in which the central
temperatures and
densities are
sufficient for steady
nuclear fusion
reactions to occur.
A star’s color is indicative of its temperature
Color
Spectral type
Temperature
Stars are often described by their “spectral type”,
which is a function of its temperature
The required mass to
have fusion reactions
in the core is at least a
few percent of the
mass of the sun.
Nuclear fusion occurs
in the core of a star.
Fusion of hydrogen to
helium is the nuclear
process functioning
over most of a star’s
lifetime.
We refer to this time as
the Main Sequence
lifetime
A convenient way to
gain insight into the
life and death of stars
is through the
“Hertzsprung-Russell
Diagram”
Hertzsprung-Russell Diagram
A plot of the temperature of stars against their brightness (luminosity)
Hertzsprung-Russell
Diagram
Stars do not fall
everywhere in this diagram
An HR diagram for about 15,000
stars within 100 parsecs (326
light years) of the Sun.
Most stars lie along the
“Main Sequence”
Hot stars (bluer) are
found at the upper left
hand end of the Main
Sequence while cooler
(redder) stars are found
to the lower right.
Stars are all classified
according to temperature and
spectral type, with the hotter
stars called ‘O’ type stars and
the coolest called ‘M’ type
stars. The order of
classification is:
O-B-A-F-G-K-M
Stars live most of
their lives on the
“Main Sequence”.
These stars
generate energy by
nuclear fusion of
hydrogen into
helium in their core.
Very
rare
Hotter “Main
Sequence”
stars are
much less
common than
cooler Main
Sequence
stars
Very
common
Hotter stars
have shorter
Main
Sequence
lifetimes than
cooler stars
107 yrs
108 yrs
109 yrs
1010 yrs
1011 yrs
A star “moves” on the HR
diagram as it ages
Collapse of
protostar to
Main
Sequence
Moving up
Main
Sequence
Hydrogen begins
to run out in core.
Expansion to
giant
Depletion of fuel in core.
Shedding of mass
Collapse of remnant
- dead star
Increasing mass
Major Factors for life on the
Surface of a Planet:
 Location, location, location:
– must lie within a star’s habitable zone
Major Factors for life on the
Surface of a Planet:
 Location, location, location:
– must lie within a star’s habitable zone
 Size is important:
– Large enough to retain an atmosphere substantial
enough for liquid water
– Large enough to retain internal heat and have plate
tectonics for climate stabilization
The Habitable Zone
An imaginary spherical shell surrounding a star
throughout which the surface temperatures of any
planets present might be conducive to the origin
and development of life as we know it.
Essentially a zone in which
conditions allow for liquid water
on the surface of a planet.
The Sun’s
Habitable
Zone
(today)
The Sun’s
Habitable
Zone
(thru time)
The Sun’s
brightness
(luminosity) has
changed with time.
Habitable Zones for Different Stars
Lower mass (cooler) stars
have smaller habitable zones
By contrast, the HZ of a highly luminous star would in principle be
very wide, its inner margin beginning perhaps several hundred
million km out and stretching to a distance of a billion km or more.
The size and location of the HZ depends on
the nature of the star
Hot, luminous stars – spectral types "earlier" than that of the Sun (G3-G9, F, A,
B, and O) – have wide HZs, the inner margins of which are located relatively
far out:
To enjoy terrestrial temperatures:
Around Sirius (Spectral type A1: 26 times more luminous than the Sun),
an Earth-sized planet would have to orbit at about the distance of Jupiter
from the star.
Around Epsilon Indi (Spectral type K5: about one-tenth the Sun's
luminosity), an Earth-sized planet would have to orbit at about the
distance of Mercury from the star.
The size and location of the HZ depends on
the nature of the star
The situation becomes even more extreme in the case of a red dwarf, such as
Barnard's Star (M4: about 2,000 times less luminous than the Sun), the HZ of
which would extend only between about 750,000 and 2 million km (0.02 to
0.06 AU).
However: if planets exist too close to its parent star, the development of
life might be made problematic because the tidal friction would have led to
synchronous rotation.
 The same side of the planet will always face the star.